I am referring to opamps, not discrete circuits, although in the end i see no difference in the effect on the headphones.

While building my cmoy based on tangent's docs i noticed just how much DC offset a bipolar opamp with large input bias current can create in a circuit not designed for it.
I didn't see the 20mV as a "right above that it'll fry" value

It just made me wonder, in my cmoy i have control over the resistors involved in the amp and i can later just for fun change their values to control the LT1364's high DC offset. But what about the people opamp rolling in amps under the assumption it's all good?

I put the LT1364 in a hybrid amp and while the LME49720 in it shows ,1mV offset, the LT1364 still almost scores 30mV. (It's btw 300mV in my cmoy using the stock resistor values, 100mV with resistor values i happened to have available).
I am impressed how well National controlled the input bias current, since i saw no other (popular) bipolar opamp reach nA range, bipolar opamps seem to be typically more in uA range.

So i was wondering, how much past the 20mV is safe, how much heat is a constant voltage in mV range causing on the driver, or is it all just affecting the dynamic range with the shifted "zero point" (offset + signal reaching the max the headphones could deal with sooner?)

I can't possibly listen to the headphones as loud as they can manage to dish out, so is the DC offset still of concern?
This might actually spill over in my decisions of buying used headphones down the road if damage is indeed a possibility.

opamps aren't designed for driving headphones directly thats why there are DC offset problems. Looking at the datasheets of most opamps they specify a minimum load of 600Ohm's or greater. Companies make dedicated headphone amplifier chips that are not much more complex to use and will work much better, I don't understand why people don't just use those.